Japanese patent application JP 2005-028121 describes a system for measuring local lung ventilation. Said system uses a 3D CT scan of the lungs at the moments of inhalation and exhalation. The inhalation image and the exhalation image are then aligned and a displacement vector field is obtained. Local lung ventilation is computed from the displacement vector field. Integration of local values is performed for obtaining a total ventilation amount. FIG. 3 of JP 2005-028121 shows a picture wherein the local lung ventilation is visualized. In this picture, areas of expansion, areas of contraction and areas having a constant volume are indicated.
It is a problem of the system of JP 2005-028121 that the output picture only provides information about the local volume change for a complete breathing cycle. More detailed information may help a doctor, therapist or researcher to make a better assessment of the physical condition of an examined lung.